Diaphragm pumps may occasionally be disconnected from their fluid sources. Upon reconnecting the pump, it must be primed in order to remove air from the plumbing connections and to prepare the pump for immediate delivery of pumped fluid when operated. Prior pump systems have typically implemented a priming function by operating the pump for a set period of time. Such priming functions, however, do not reliably achieve prime. For instance, the pump may not actually achieve prime during the set period of time, in which case the priming function has failed. Alternatively, the pump may achieve prime before the end of the set period of time, in which case excess fluid will be pumped downstream and wasted.